The present invention relates generally to medical methods, apparatus and systems. More specifically, the invention relates to methods, apparatus and systems for enhancing cardiac pacing.
Defects in the electrical conduction system of the heart can lead to a number of potentially life-threatening conditions, such as congestive heart failure (CHF), a fatal cardiac arrhythmia or the like. Implantable devices used to provide electrical pacing of a heart to treat defects in the heart's conduction system, typically called cardiac pacemakers, are known. Such implantable devices work in a variety of ways and may provide electric pulses to multiple areas of a heart. Biventricular pacing devices, for example, provide pulses to both the left and right ventricles of the heart using multiple leads.
In many instances, it may be advantageous to provide cardiac pacing to a heart in a desired timing sequence, with electric pulses having a desired duration or pattern or the like, to result in a desired pattern of contraction of the heart. In some cases of CHF, for example, it may be desirable to allow for increased filling time of the left ventricle to enhance cardiac output and ejection fraction. If the ventricle contracts too early, cardiac output will typically be less than might be achieved with a slightly delayed contraction. In some instances, it may be advantageous for the right and left ventricles to contract simultaneously, while in other cases it may be better for one ventricle to contract slightly ahead of the other. It may also be advantageous to control the timing of contractions of the right and left atria relative to one another as well as to the ventricles. Many different combinations of pacing patterns might be desirable for a variety of different patients, different activity levels and the like.
Cardiac pacing devices have certainly improved the treatment of cardiac conduction defects, but currently available devices still have certain shortcomings. For example, currently available biventricular and other pacing devices typically do not allow for significant (or in some cases any) adjustment. What little adjustment is possible typically involves a time-consuming process that is neither as objective or as accurate as would be desirable. To adjust the timing of a biventricular pacing device, for example, a cardiologist will typically fire the pacing device with a first timing sequence, while a second physician or technologist images the patient's heart during the cardiac cycle using an ultrasound device. Vector measurements are then manually made on the ultrasound images, and a computer is used to approximate cardiac performance from the vector measurements. This process may take as long as fifteen to thirty minutes, just to assess one timing sequence of the pacing device. To compare multiple timings of the pacing device may take several hours spent in a cardiology clinic, which is inconvenient for the patient as well as inefficient for the cardiologist and technician. Furthermore, even after several hours the physician only has data for a few different possible settings of the pacing device, and that data relies on the accuracy of manual measurements performed by the technician. This is just one example of the limited adjustability of today's cardiac pacing devices, but it is typical.
Additionally, once a patient leaves the clinic, any additional adjustments typically require a return visit to the cardiology clinic and another lengthy adjustment process as described above. Thus, it is often difficult to adjust a pacing device to optimize cardiac performance (cardiac output, ejection fraction, and the like) in an individual patient. Similarly, it is also difficult to optimize parameters of the pacing device itself, such as energy consumption which determines battery life, using currently available devices and methods.
Therefore, it would be desirable to have methods, apparatus and systems for enhancing cardiac pacing. Ideally, such methods, apparatus and systems would facilitate measurement of one or more cardiac characteristics and adjustment of a cardiac pacing device to allow a physician to conveniently assess performance of the pacing device at various settings. Such methods, apparatus and systems would allow a physician to select a timing sequence for a pacing device, such as a delay between firing of left-sided and right-sided leads in the heart, to achieve a desired level of cardiac performance. Also ideally, such adjustments would not only enhance cardiac pacing, and thus overall cardiac performance, but they would also enhance the performance of the cardiac pacing device itself. At least some of these objectives will be met by the present invention.